How Does Remote Sensing Work?

In order to measure a vehicle’s most representative exhaust emissions (i.e. that which can be used to judge a vehicle’s emissions health and compliance with in-use standards), RSD test sites are typically located at highway on-ramps and other locations where vehicles can be found accelerating or driving under engine load at a moderate speed.

As a vehicle passes by, the RSD equipment is able to complete a test record, including measuring and analyzing the vehicle’s exhaust, in less than one second.

Here’s how RSD works: (See figure below for numbered references.)

The vehicle first passes through speed and acceleration detectors (3), while an image of the license plate is taken (5) to match the vehicle tag with the registration record.

The vehicle then passes through safe, low intensity infrared and ultraviolet light beams of the emissions analyzer. A safe laser light source (2) directs the beams across the road, where they are reflected off mirrors (1) and directed back to a detector module.

As the light beams intersect with the vehicle’s exhaust plume, the detector module employs light absorption spectroscopy to measure the levels of carbon monoxide, carbon dioxide, hydrocarbons, oxides of nitrogen and particulate matter in the exhaust.(4) The emissions readings are matched to the license plate and an official test record is created and compiled for RSD Data Applications.

To ensure accurate, uncontaminated readings, RSD’s do not operate during rain, snow, high winds or other adverse weather conditions.